The invention relates to an apparatus for shielding an electronic circuit situated on a printed circuit board in an electrically conductive housing which has at least one opening and/or bushing.
In electronic equipment, interference and faults can occur on account of electromagnetic radiation from external sources. Particular weak points in this case are the bushings of connection pins through the electrically conductive housing surrounding the electronic circuit, and also the connection pins themselves.
It is an object of the present invention, therefore, to improve the shielding in the region of openings and bushings of the housing.
This object is achieved according to the invention by virtue of the fact that a shielding tube extends from the printed circuit board as far as the housing and encompasses the opening and/or the bushing, and that a device for length equalization of the shielding tube forms an electrical contact of the shielding tube independently of tolerances between the printed circuit board and the housing.
The apparatus according to the invention has the advantage that the region around the opening and/or bushing and around the connection pins is completely shielded from the circuit. Furthermore, the shielding is effected independently of the actual distance between printed circuit board and housing within given tolerances. The invention can be applied to all metallic and metallized housings.
A first advantageous refinement of the invention consists in the fact that the device for length equalization is formed by the shielding tube being resilient in the longitudinal direction. In this case, the shielding tube can be dimensioned in such a way that, for all distances manifested between the housing and the printed circuit board, it exerts a pressure which is required for reliable contact with the housing. Preferably, at least part of the shielding tube is in bellows form.
Further advantageous refinements of the invention consist in the fact that the device for length equalization is formed by a peripheral web arranged on the housing, the shielding tube engaging into said web or which web is encompassed by the shielding tube.
For the purpose of reliable contact-making and reliable sealing, in these refinements it may be provided that the shielding tube is provided with a flange, which serves as contact area and is directed toward the peripheral web.
A contribution to inexpensive production of the apparatus according to the invention is made by the fact that the peripheral web is connected in one piece to the housing. In the invention, however, it may also be provided that the peripheral web is part of a plug apparatus.